Researches on Irritability of Plants Sir J C Bose

8/6/2019 Researches on Irritability of Plants Sir J C Bose

1/407


2/407

&> &


3/407


4/407


5/407

RESEARCHES ON IRRITABILITY OF PLANTS


6/407

WORKS BY THE SAME AUTHOR.RESPONSE IN THE LIVING AND NON-LIVING.

With 117 Illustrations, 8vo., iar. 6d. 1902.PLANT RESPONSE: AS A MEANS OF PHYSIO-LOGICAL INVESTIGATION. With 278 Illustra-

tions, 8vo., 2 1j. 1906.COMPARATIVE ELECTRO - PHYSIOLOGY:A PHYSICO-PHYSIOLOGICAL STUDY. With

406 Illustrations, 8vo., l$s. 1907.LONGMANS, GREEN, AND CO.

London, New York, Bombay, and Calcutta


7/407

RESEARCHES ONIRRITABILITY OF PLANTS

BY

JAGADIS CHUNDER BOSE, M.A. D.Sc. C.S.I.PROFESSOR, PRESIDENCY COLLEGE, CALCUTTA

WITH ILLUSTRATIONS

LONGMANS, GREEN, AND CO.39 PATERNOSTER ROW, LONDON

NEW YORK, BOMBAY, AND CALCUTTA1913


8/407

QXL17!


9/407


10/407


11/407

PREFACEI have in this work dealing with my researches on theirritability of plants introduced new methods by whichthe scope of investigation has been enlarged, and a veryhigh degree of accuracy secured. In my previous treatiseon Plant Response, the response recorder employed was amodification of the optical lever, automatic records beingsecured by the very inconvenient and tedious process ofphotography. The delay thus imposed retarded seriouslythe progress of the research. Those practically engaged ininvestigations on plants can realise the difficulties thatarise from the too quick passage of the seasons. It thusfrequently happened that by the time new instrumentalappliances were rendered practicable the favourable seasonfor the plant was over, involving the postponement of theexperiment for another year. In spite of these difficulties,the long series of investigations that I then carried out gavemany interesting results, which not only threw light onmany obscure problems, but also led to the discovery ofseveral important phenomena in plant physiology.

Some of these results, moreover, tended to cast doubton certain conclusions that had found universal acceptance.It has, for example, been held that there was no trans-mission of true excitation in Mimosa, the propagatedimpulse being regarded as merely hydro-mechanical. Thequestion whether the transmitted impulse was physical orphysiological could only be satisfactorily decided if theplant could itself be made to record the velocity of itsimpulse and the changes induced in that velocity underphysiological variations. This is but one out of several


12/407

viii RESEARCHES ON IRRITABILITY OF PLANTSideal methods of attacking problems in the life of plants,the realisation of which would make a great advance inphysiological investigation.

It would also be desirable to discard, if possible,*" thetroublesome method of obtaining record by photography,which necessitates work in a dark room ; in this connectionit should be remembered that subjection of the plant todarkness introduces complications by modifying its normalexcitability. For these reasons, another requirement whichit is necessary to fulfil is the devising of some simple anddirect method of obtaining the record. And in order thatthe results obtained should not be influenced by any personalfactor, it would be further desirable that the plant attachedto the recording apparatus should be automatically excitedby stimulus absolutely constant, should make its ownresponsive record, going through its own period of recovery,and embarking on the same cycle over again withoutassistance at any point on the part of the observer.

The difficulties encountered in realising these idealrequirements appeared at first to be insurmountable. In therecords of response serious errors occurred as regards ampli-tude and time-relations, owing to the friction of the writinglever against the recording surface. As an extreme instanceof this, in recording the rhythmic movement of the leafletsof Desmodium the very slight friction which the smoked-glass surface offered was enough to stop the pulse-record.

After many attempts, I was at last successful inovercoming all obstacles by the device of the Resonantand Oscillating Recorders. Taking the very difficult testof direct record of the rhythmic movements of Desmodiumleaflets, it will be found that the pulsations recorded in thisbook not only gave accurate measure of the amplitude andperiod, but also the absolute rate of movement during anyphase of their autonomous response. Again, in the matterof accurate measurement of short intervals of time requiredfor the determination of the latent period and velocity oftransmission of excitation, I have shown the possibility


13/407

PREFACE ixof recording time-intervals as short as a thousandth part ofa second. A brief account of this is given in my paper" On an Automatic Method for the Investigation of theVelocity of Transmission of Excitation in Mimosa," readbefore the Royal Society. It will be recognised immediatelyin how many directions our power of inquiry has becomeextended by the elaboration of these new methods andthe invention of several types of instrumental appliancesdescribed in this work. '

In presenting the results of these investigations, it willbe noted that the plant has been made to tell its own story,by means of its self-made records. Each experiment hasbeen repeated at least a dozen times, in many cases as oftenas a hundred times. The results may therefore be acceptedas fully attested. The establishment of the unity of re-sponsive reactions in the plant and animal, which is thesubject of this work, will be found highly significant, since itis only by the study of the simpler phenomena of irritabilityin the vegetal organisms that we can ever expect to elucidatethe more complex physiological reactions in the animaltissues.

I take this opportunity to thank my research assistants,Messrs. Guruprasanna Das, L.M.S., and Surendra ChandraDas, M.A., for the very efficient help rendered by them inthese researches.

J. C. BOSE,Presidency College, Calcutta,

October 1912.


14/407


15/407

CONTENTSCHAPTER IPLANT SCRIPTS

PAGEAction of environment on plantRevelation of internal conditionby character of responseProblems to be solvedElectricalresponseMechanical responseMotile organ in MimosapudicaResponse in plant and animalDifferent phasesof the responsive movementGraphic recordDeterminationof absolute movement of leaf and its time-relationsCharacteristic effects of different agencies on the response-curveSpecific difficulties in recording plant-response . i

CHAPTER IITHE RESONANT RECORDER

Advantages of intermittent contact in recordTwo types ofapparatus : the Oscillating Recorder, and the ResonantRecorderCoercer and VibratorPerfect tuningRecorderswith standardised frequenciesSlide and clockworkTherecord its own chronogramSmoked surface and its fixationAdjustments of the writerRecords with continuous andintermittent contacts ....... 1

CHAPTER IIIMETHODS OF STIMULATION

Different methods of stimulating the plant : mechanical, chemical,thermal and electricalDifficulties of securing quantitativestimuliDirect and indirect stimulationIdeal modes ofstimulationElectro-thermic stimulationStimulation byconstant currentStimulation by condenser-dischargeNon-polarisable electrodesDirect, extra-electrodal, and intra-electrodal stimulationStimulation by induction-shockEffects of make- and break-shockExcitation by tetanisingshock .......... 23

xibz


16/407

xii RESEARCHES ON IRRITABILITY OF PLANTSCHAPTER IV

TIME-RELATIONS OF THE RESPONSIVE MOVEMENT ANDSTANDARDISATION OF STIMULUSPAGE

Latent period of MimosaApex timeRate of responsive move-ment of leafEffect of intensity of stimulus, fatigue, andtemperaturePeriodic dot markerTime relations of responseand recoveryEffect of seasonResponse of BiophytumResponse of NeptuniaAbitrary distinction between sensi-tive and ordinary plantsDifferential response in MimosaResponse of ordinary plantsUniversal sensitiveness ofplantsStandardisation of stimulusMaximal and MinimalStimuliExtreme sensitiveness of Mimosa.... 35

CHAPTER VTHE ADDITIVE EFFECT ; INFLUENCE OF LOAD, TEM-

PERATURE, AND INTENSITY OF STIMULUSGreater excitatory efficiency of the break-shockAdditive effectof stimulusQuantitative relation of additive effectEffect

of loadThermal chamberEffect of temperatureEffect ofincreasing intensity of stimulus on response ... 52

CHAPTER VIVARIOUS TYPES OF RESPONSE

Necessity of uniform stimulationThe Periodic StarterTheAutomatic ExciterElectrolytic contact-makerThe com-plete Response-recorderThe factor of tonicityUniformresponsesFatigue under shortened period of restGrowingfatigueAlternating fatigueStaircase responseExplana-tion of erection of leaf under continuous stimulationFatigue-relaxation in plant and animalResponse under single stimulusand under tetanisation ....... 64

CHAPTER VIIEFFECTS OF DIFFERENT GASES ON EXCITABILITY

OF MIMOSAInduced change of excitability under sudden variation of light

Abolition of excitability by absorption of waterRestorationof excitability by application of glycerineStimulating,


17/407

CONTENTS xiiidepressing, and toxic agentsPhenomenon of accommodation

Stimulating action of ozoneEffects of carbonic-acidgas, vapour of alcohol, ether, carbon disulphide, coal gas,chloroform, ammonia, sulphuretted hydrogen, laughing-gas,nitrogen dioxide, and sulphur dioxide . . . - . 85

CHAPTER VIIIDEATH-SPASM IN PLANTS

Criterion of the death of plantAbolition of electric response atdeathMechanical spasm of deathWater-bath for uniformrise of temperatureExcitatory effect of sudden cooling orheatingErection of leaf with rising, and depression of leafwith falling, temperatureThermo-mechanical inversionat the death-pointNecessity for specification of rate of riseof temperature Death-record of Mimosa Abolitionof response after death-spasmConstancy of death-pointexhibited by different specimens Death-records ofDesmodium gyrans and Vicia FavaDeath-spasm in ordinaryplantsThe electric-spasm of deathLowering of death-point by fatigue and by poisonous solution ....

CHAPTER IXDETERMINATION OF THE LATENT PERIOD

Difficulties of accurate determination of Latent PeriodAdvan-tages of Resonant RecorderSimultaneous tracings of tuning-fork exciter and Resonant RecorderAutomatic stimulationat a definite momentIdentical value of latent period insuccessive determinationsAccurate measurement of time-interval shorter than .005 secondLatent period little affectedby inertia of recorderTabular statement of value of differentspecimens of MimosaEffect of season on latent period . 108

CHAPTER XINFLUENCE OF INTENSITY OF STIMULUS, FATIGUE,AND TEMPERATURE ON THE LATENT PERIOD

Diffuse stimulation under alternating-shockEffect of intensityof stimulus on Latent PeriodInfluence of optimum conditionEffect of fatigueEffect of temperature ....


18/407

xiv RESEARCHES ON IRRITABILITY OF PLANTSCHAPTER XI

VELOCITY OF TRANSMITTED IMPULSE IN PLANTS PAGEDetection of transmitted excitation by means of electromotivevariationSpecific tissue for conduction of excitationHydro-mechanical theory of transmission of stimulusPropagation ofexcitatory protoplasmic changePhysiological testAuto-matic record of transmission-periodConditions for obtainingconstant velocityDetermination of velocity of transmissionin MimosaDifferential method of determining velocityConstancy of resultsTabular statement of different deter-minations of velocityEffect of intensity of stimulus onvelocity of transmissionEffects on sub-tonic tissue and ontissue in optimum conditionAfter-effect of stimulus inenhancing conductivityEffect of optimum condition-Disturbing action of leakage of exciting currentEffect offatigueEffect of temperatureVelocity of transmission inBiophytum and AverrhoaDirection of preferential conduction 132

CHAPTER XIIEXCITATORY CHARACTER OF TRANSMITTED

IMPULSE IN PLANTSThe hydro-mechanical theoryInconclusive character of the

anaesthetic experiment of Pfeffer and scalding experiment ofHaberlandtKiihne's experiment showing transmission ofexcitation under intense stimulation in a rigored nerveError introduced by employment of excessive intensities ofstimulusDiscriminative polar effect of current in excitationBlock of transmission of excitation by local application ofcoldRestoration of normal conductivity by tetanising shockin tissue paralysed by coldElectro tonic arrest of excitatoryimpulseAction of various poisons in inducing block of con-duction .......... 154

CHAPTER XIIITHE POSITIVE RESPONSE

Two opposite kinds of responses, negative and positiveExcitatorycontraction, negative turgidity variation, fall of leaf, andconcomitant negative electric variationPositive electricresponsePositive or erectile mechanical responseDualimpulses under different forms of stimuliExhibition ofpositive and negative impulses by different plantsCon-ditions for obtaining positive responseCharacteristics ofpositive impulseMasking and unmasking of positive effectLaws of Direct and Indirect effects of stimulus . . . 176


19/407

CONTENTS xvCHAPTER XIV

POLAR EFFECTS OF ELECTRICAL CURRENT INEXCITATION OF PLANTSPAGE

Polar excitation in animal tissuesAnomalous reactions in Pro-tozoaMono-polar methodCurrent ReverserExcitatorypolar action in plantMethod of recordEffects of ascendingand descending currents in animal and plantRecords givingtime-relationsPotential slideMeasurement of e.m.f. andcurrentPotential keyboard . . . . . . 198

CHAPTER XVPOLAR EFFECTS OF FEEBLE AND MODERATE CURRENTSON VARIOUS SENSITIVE PLANTS

Polar effects of feeble and moderate currents on (1) leaflets ofMimosa, (2) leaflets of Biophytutn, (3) leaflets of Neptunia,(4) leaflets of Averrhoa carambola, (5) leaflets of Averrhoabilimbi, and (6) primary leaf of MimosaExcitation withfeeble current only at kathode-makeExcitation at kathode-make and anode-break, under moderate currentTabularstatement of results . . . . . . . . 212

CHAPTER XVITHE CONTRASTED EFFECTS OF ANODE AND KATHODE

Polar effects of currents on pulsation of Desmodium gyransReduction of systolic contraction by anodic actionDiminu-tion of diastolic expansion by kathodic actionArrest atsystole by make of kathode and diastolic expansion by breakof kathodeArrest at diastole by make of anode, and systoliccontraction by break of anodeEffects of ascending anddescending currents of feeble and strong intensity in nerve-and-muscle preparationParallel effects in petiole-and-pul-vinus .......... 234

CHAPTER XVIIEFFECT OF TEMPERATURE ON POLAR EXCITATION, ANDMULTIPLE EXCITATION UNDER CONSTANT CURRENT

Excitability of nerve to induction-shock diminished by coolingNerve excitation by constant current enhanced by coolingExcitation of conducting-tissue of Mimosa by constantcurrent enhanced by cooling and depressed by warmingIneffective stimulus becoming effective under cooling and vice


20/407

xvi RESEARCHES ON IRRITABILITY OF PLANTSPAGE

versa Multiple response induced in Biophytum by thepassage of constant currentComparison of sensitiveness ofplant and animalMinimum current for excitation of humantongueRelatively higher sensitiveness of Biophytum . . 244

CHAPTER XVIIIPOLAR EFFECTS UNDER STRONG CURRENTS

Abnormal polar reactions in ProtozoaTransformation of polarreaction in leaf of Mimosa from Type II. to Type III. understrong currentFurther transformation to Type IV. understronger currentExhibition of Type III. and T}-pe IV. byleaflets of Mimosa, Biophytum, Averrhoa carambolaLawof polar action of strong currents . . . . . 253

CHAPTER XIXVARIATION OF POLAR REACTION UNDER TISSUE

MODIFICATIONModification of polar reaction under tissue-changesEffect ofageAfter-effect of moderate stimulationModified polar

effect ; excitation at kathode-make and anode-make ; excita-tion at kathode-make, kathode-break, and anode-makeGeneral review of polar reactions ..... 266

CHAPTER XXMULTIPLE AND AUTOMATIC RESPONSEThe Oscillating RecorderLatent period of BiophytumRefrac-

tory periodResponse on ' all-or-none ' principleMultipleelectrical response to a single strong stimulusMultiplemechanical response to strong stimulus in Biophytum andA verrhoaContinuity of multiple and automatic responseOrdinarily responding Biophytum converted into automaticallyresponding condition by excess of stored energyAutomati-cally responding Desmodium converted to ordinarily respond-ing condition by depletion of stored energy . . . .278

CHAPTER XXITHE AUTOMATIC PULSATIONS OF DESMODIUM GYRANS

Activity of detached leaflet of DesmodiumPulsation maintaineduniform under constant internal hydrostatic pressureTheplant-chamberTime-relations of pulsating movement derived


21/407

CONTENTS xviifrom dotted recordSignificance of down and up movementsSystole and diastoleTable showing rates of movement ofDesmodium leaflet at different phases .... 290

CHAPTER XXIIEFFECT OF HYDROSTATIC PRESSURE, LOAD, AND LIGATUREON THE PULSATION OF DESMODIUMEffect of internal hydrostatic pressure on the pulsation of Desmo-

diumExpansive erection of leaflet under increased pressure ;diminution of the extent of systolic contractionEffect ofload : diminution of periodStannius' ligature on heart-beatParallel effect of ligature on pulsation of DesmodiumArrest of pulsation by a cut and revival by electric shock . 300

CHAPTER XXIIIEFFECT OF STIMULUS ON LEAFLET OF DESMODIUM

AT STANDSTILLCondition of standstill brought about by depletion of energy

Renewal of pulsation by the stimulus of lightResponse tostimulus of induction-shockMultiple response under tetani-sationDetermination of the latent period and the apex timeRefractory periodEffect of stimulus on leaflets in sub-tonic conditionEffect of isolation on rhythmic activityGradual arrest of pulsation resulting from run-down of storedenergyEffect of fresh accession of energy . . . 306

CHAPTER XXIVEFFECT OF ELECTRIC STIMULATION ON THE PULSATIONOF DESMODIUM GYRANS

Effect of electric shock on Desmodium leafletIncapability oftetanusExtra pulsation induced by electric shockRelativeeffectiveness of electric stimulus at diastolic phaseEffect oftransmitted excitation on normal pulsation of heart andon pulsation of Desmodium leafletEffects of accelerationand inhibition ........ 318


22/407

xviii RESEARCHES ON IRRITABILITY OF PLANTSCHAPTER XXV

EFFECT OF TEMPERATURE ON RHYTHMIC PULSATIONOF DESMODIUM GYRANSPAGE

Effect of lowering of temperature on rhythmic pulsation of cardiactissueSimilar effect on the pulsation of DesmodiumIncrease of systolic limit during coolingMinimum tempera-ture for arrest of pulsationArrest by cooling and subsequentrevival by warmingIncrease of diastolic limit duringwarmingEffect of rise of temperature on the pulsation offrog's heartSimilar effect on the pulsation of DesmodiumEffect of rise above and return to normal temperatureDiminution of systolic contraction during rise of temperatureIncrease of systolic contraction during fall of temperaturePermanent arrest due to heat-rigor . . . . . 323

CHAPTER XXVIEFFECT OF CHEMICAL AGENTS ON THE AUTOMATIC

PULSATION OF DESMODIUM GYRANSApplication of gaseous or liquid reagentsModifying influence of

tonic condition of specimen, strength, and duration of appli-cationEffect of sugar solution-Effect of alcoholActionof carbonic-acid gasEffects of anaesthetics, ether, and chloro-formAction of carbon disulphideEffect of copper sul-phate solutionEffect of potassium cyanide solutionAnta-gonistic actions of acids and alkalis on the pulsations ofthe heart and of DesmodiumSimilarities of reaction inrhythmic tissues animal and vegetal ..... 332CHAPTER XXVII

GENERAL SURVEY . . . 342Classified List of Experiments ..... 361Index .......... 369


23/407

ILLUSTRATIONSFIGlI.2.3-4-5-6.7-8.9-

io.ii.12.13-14.15-16.17-

19.20,22,26.27.293031323334353637

Diagrammatic representation of Response RecorderResponse curve of leaf of MimosaResonant Recorder, upper part ....General view of the Resonant Recorder and accessoriesRecord showing advantage of intermittent contactElectro-thermic stimulator .....Response of Mimosa to indirect thermal stimulationResponse to stimulus of constant electric current .Direct stimulation by condenser dischargeRecord of response to stimulation by condenser dischargeArrangement for applying single make- or break-shockRecords giving apex time of response of MimosaThe dot marker......Response of Mimosa giving time-relationsRecord of response of leaflet of Biophytum .Response of leaf of NeptuniaErectile response of leaf of Mimosa, due to local stimulation

upper half of pulvinus....Responses of leaf of Desmodium gyransThe electric signal .....

21. Records showing greater efficiency of break-shock23, 24, 25. Additive effects of stimulusEffect of load on response of Mimosa .

28. Effect of temperature on response of MimosaIncreasing response under increasing stimulationPeriodic starter, and automatic exciterElectrolytic contact-maker ....Photograph of duplex type of Resonant RecorderUniform responses of MimosaFatigue under shortened period of restGrowing fatigue ......Periodic fatigue ......Staircase response in frog's muscle

xix

PAGF67

17202125262728303238404i4343

45465253

54-5657

60, 61626668697273747477

of


24/407

xx RESEARCHES ON IRRITABILITY OF PLANTSFIGURE PAGE38. Staircase response in Mimosa ...... 7739. Effect of stimulus in modifying the tonic condition . . 7940. Alternating response . . . . . . . .8141. Fatigue-decline in frog's muscle . . . . . .8142. Different phases in the fatigue reversal in plant ... 8343. Fatigue reversal in Mimosa. ...... 8344. Effect of sudden darkness on excitability of Mimosa45. Abolition of motile excitability of pulvinus by absorption of 86

water 8846. Stimulating action of ozone ...... 9047. Effect of CO- on excitability of Mimosa .... 9048. Effect of vapour of alcohol....... 9149. Effect of ether ......... 9250. Effect of carbon disulphide ...... 9351. Effect of coal gas ........ 9352. Abolition of excitability under chloroform .... 9453. Effect of ammonia ........ 9554. Effect of sulphuretted hydrogen ...... 9555. Effect of nitrogen dioxide ....... 9656. Effect of sulphur dioxide ....... 9657. Excitatory effect on Mimosa by sudden cooling or warming . 10058. Death-curve of Mimosa ....... 10259. Abolition of response to warming or cooling after passing through

the death-point . . . . . . . .10360. Death-curve of Desmodium gyrans . . . . .10461. Thermo-mechanical inversion indicating death-point of leaf of

bean .......... 10562. Lowering of death-point under fatigue . . . . .10663. Effect of poison in lowering the death-point . . . .10664. Latent period of hyoglossus muscle . . . . .10965. Simultaneous record of vibrating recorder and exciting tuning

fork no66. Apparatus for determination of latent period of Mimosa . 11267. Two successive records exhibiting identity of latent period of

Mimosa . . . . . . . . .11568. Record of latent period of highly excitable Mimosa . .11669. Record of latent period with a 200 D.V. recorder . . .11770. The same record magnified . . . . . . .11871,72. Two records obtained with two different recorders . . 11973. Record of latent period of Neptunia . . . . .12074. Simultaneous excitation in interposed tract under alternating-

shock . . . . . . . . . .12475. 76. Effect of intensity of stimulus on latent period . . .126


25/407

ILLUSTRATIONS xxi77. Constancy of latent period under stimuli above the maximal78, 79. Effect of fatigue .......80, 81. Effect of temperature ......82. Determination of velocity of transmission of excitation in

Mimosa ........83, 84. Determination of velocity by Differential Method . 139, 14085 Effect of intensity of stimulus on velocity and after-effect

Effect of optimum condition on velocityEffect of fatigue on velocity of transmission .Effect of temperature on velocity ....Record giving transmission time in Biophytum

90. Effect of cold in the retardation and arrest of transmission91. Arrangement for electrotonic block ....92. Record of effect of electrotonic block ....93. Records of transmitted excitation with the block off and on94. Effect of CuS04 in abolishing conduction95. Abolition of conductivity by'KCN . ...96. Positive response followed by negative in Biophytum under

indirect thermal stimulus .....97. Diphasic response in Biophytum under indirect chemicalstimulation .......98,99. Positive followed by negative in A verrhoa .100. Diphasic response in Mimosa due to indirect electric stimu

lation of petiole.......101. Diphasic response in Mimosa due to indirect thermal stimu

lation of stem .......102. Effect of intensity of stimulus in modifying the diphasic response 187103. Effect of diminishing distance in transforming positive into

diphasic response in Biophytum . . . . .189104. Effect of diminishing distance on the response in Mimosa . 194105. Masking of the positive by the predominant negative . .194106. Pohl's commutator ........ 200107. Record of polar excitation under feeble current . . . 202108. Excitation by ascending and descending current . . . 204109. Records of responses to ascending and descending current

in Mimosa......... 205no. Records of responses to ascending and descending induction-shock ......... 206in. The Potential Slide 208112. The Potential Keyboard . . . . . . .210113. The electrode holder

.

. . . . . . .217114. Excitation induced in Biophytum by the make of kathode and

break of anode ........ 224

127128130

137

143145147149151162165166167172173

180182184

186


26/407

xxii RESEARCHES ON IRRITABILITY OF PLANTSFIGURE. PAGE115. Record of kathode-make and anode-break in Mimosa . .230116. Effect of anode, opposing systolic contraction in Desmodium . 236117. Effect of kathode, opposing diastolic expansion in Desmodium 236118. Alternate effect of anode and kathode . . . -237119. Arrest at systole by make of kathode, and diastolic expansion

at break of kathode . . . . . . .237120. Arrest at diastole by make of anode, and systolic contraction

at break of anode ....... 237I2i. Effects of descending and ascending currents at make and

break on nerve-muscle and petiole-pulvinus . . .239122. Effect of cold on excitability to induction-shock . . . 246123. Record showing abolition of polar excitation at high tem-

perature ......... 247124. Multiple excitation in Biophytum under constant current . 249125. Record of polar excitation of Type III. .... 255126. Polar excitation Type IV. . . . . . . .256127. Transformation of Type II. to Type III. as after-effect of

previous stimulation ....... 268128. Abrupt transition from Type I. to Type III. . . . 271129. Polar reactions, Km, Km Am, and Km Am Ab under gradually

increasing current . . . . . . .273130. Record exhibiting modified response Km Kb Am . . . 275131. The Oscillating Recorder . . . . . . .279132. Record giving latent period of Biophytum .... 281133. Record of responses of Biophytum to stimuli -i and 1 unit . 282134. Responses of Biophytum to stimuli .1, .5, 1, and 2 units . . 284135. Multiple response in Biophytum under strong electric shock 284136. Multiple response in Averrhoa under a single strong electric

shock ......... 285137. Multiple response under constant stimulus of light . . . 285138. Multiple response under single strong thermal shock . . 286139. Multiple response induced by strong chemical stimulation . 287140. Leaf of Desmodium gyrans....... 290141. U-tube support and plant-chamber ..... 292142. Continuous record of pulsations of Desmodium leaflet for four

hours ......... 294143. Record of a single pulsation of Desmodium giving time-relations 296144. Record of two successive pulsations ..... 297145. Series of automatic pulsations of Desmodium . . . 298146. Effect of application of increased internal hydrostatic pressure

on the pulsation of Desmodium ..... 301147. Effect of increasing load on Desmodium pulsation . . . 302148. Effect of ligature in inducing arrest of pulsation of Desmodium 303


27/407

ILLUSTRATIONS xxmFIGURE149.I50.151-

Arrest of pulsation by cut and revival by electric shock .Action of light in renewing pulsation of DesmodiumResponse of Desmodium leaflet, originally in a state of stand-

stillMultiple response under tetanisation .....Response of Desmodium exhibiting apex timeRecord exhibiting refractory period in DesmodiumAfter-effect of stimulation on pulsation of Desmodium in sub-

tonic condition ........Effect of depletion of energy on pulsation of isolated

Desmodium .........Gradual stoppage of pulsation in isolated leaflet of DesmodiumEffect of stimulus in renewing pulsation of Desmodium,brought to standstill .....

Response of Desmodium leaflet to stimulus of lightResponse of a depressed specimen of Desmodium .Effects of strong tetanisation on Desmodium pulsation

162, 163. Extra pulsation induced by induction-shock applied atdiastolic phase .....Inhibitory effect of transmitted excitation on the pulsationof vigorous leaflet of Desmodium

Augmentation of pulsation induced by transmitted excitationin less vigorous specimen of Desmodium

Effect of lowering of temperature on the pulsation of heartEffect of lowering of temperature on pulsation of Desmodium

168, 169. Effect of rapid cooling on Desmodium pulsation170. Effect of rise of temperature on amplitude and frequency of

pulsation of the heart of frog172. Effect of rise of temperature on the pulsation of DesmodiumEffect of continuous rise of temperature from 30 C. to 38-5 CEffect of continuous rise from 30 C. to 42 C. and return to

30CEffect of rise of temperature and returnEffect of dilute sugar solution .Effect of alcohol on the pulsation of DesmodiumEffect of internal application of strong alcoholEffect of dilute carbonic-acid gasEffect of strong carbonic-acid gasEffect of internal application of carbonic acidEffect of vapour of ether ....Effect of vapour of chloroform .

184. Effect of carbon disulphide185. Effect of copper sulphate solution

152.153-154-155-

156.

157-158.

159.160.161.

164.

165.

166.167.

i7ii173-174.

175-176.177.178.179.180.181.182.183.

PAGE3043073083083093IO

312

313313

3153l63l6318

319320

321324325326

327328329

330330333333334334335335336337337338


28/407

xxiv RESEARCHES ON IRRITABILITY OF PLANTSFIG. PAGE186. Effect of potassium cyanide ...... 339187. Arrest of pulsation of the heart of frog at diastole by the

action of dilute lactic acid ...... 339188. Arrest of pulsation of Desmodium at diastole by applicationof dilute lactic acid ....... 340

189. Arrest of pulsation of heart at systole, by the action of dilutesodium hydrate . . . . . . . .340

190. Arrest of pulsation of Desmodium at systole by the applicationof dilute solution of sodium hydrate .... 340


29/407

RESEARCHES ON IRRITABILITYOF PLANTSCHAPTER IPLANT SCRIPTS

Action of environment on plantRevelation of internal condition bycharacter of responseProblems to be solvedElectrical responseMechanical responseMotile organ in Mimosa pudicaResponsein plant and animalDifferent phases of the responsive move-mentGraphic recordDetermination of absolute movement ofleaf and its time-relations Characteristic effects of differentagencies on the response-curve Specific difficulties in recordingplant-response.

In strong contrast to the energetic animal, with its variousreflex movements and pulsating organs, stands the plantin its apparent placidity and immobility. Yet that sameenvironment, which with its changing influences so strikinglyaffects the animal, is playing upon it also. Storm andsunshine, the warmth of summer and the frost of winter,drought and rain, all these and many more come and goabout it. What coercion do they exercise upon it ? Whatsubtle impress do they leave behind ? That they, in theirtotality, do leave the plant better or worse for their occur-rence, we know. It is evident that internal changes areeffected by their agency which are entirely beyond ourvisual scrutiny. Would it be possible to trace this generalaction of the environment into some detail, and then followout the question of its particular effects upon the vegetalorganism ? Is there any means by which we might find out


30/407

2 RESEARCHES ON IRRITABILITY OF PLANTSwhether a given influence has contributed to the plant'swell-being or the reverse, whether it has left it moreor less excitable, whether it has rendered it more or lessenergetic ?

It is conceivable that internal changes which eluded ourdirect vision might nevertheless be brought within therange of our observation if we could obtain any sort ofanswer from the plant itself to a questioning shock. Insuch a case, the feebleness or vigour of the reply would initself doubtless constitute a measure of the vitality of theorganism. It appears obvious that if any given influence hadrendered the plant more excitable, this fact would be mani-fested by the greater intensity of its response. In a veryexcitable condition we may suppose the slightest shock ofstimulus would evoke a very large responsive expressionin a state of depression, on the other hand, the strongeststimulus would induce only a feeble reply. The relationbetween the stimulus and the response would thus form agauge of the physiological condition of the organism. Theinvisible fluctuating changes taking place in the plant, underthe changing conditions of the environment, might in thisway be made to reveal themselves.

All this presupposes, however, that the plant will answerin some tangible way to the impinging testing stimulus,and that it may be possible to obtain some record of thisanswer. The possibility of this will be further discussedpresently. There are many important problems which waitfor their solution till some such means of inquiry is found.What, for instance, are the various forms of stimulus whichevoke an answering reaction in the plant ? Again, has agiven plant-tissue, like animal muscle, any definite percep-tion-period capable of exact measurement ? Is the respond-ing tissue susceptible of fatigue ? Is the intensity of itsanswer dependent on the intensity of the blow ? Is theexcitation that may be caused at one point transmissibleto a distance, as along animal nerve ? Is such transmission,supposing it to occur, fundamentally of the same nature


31/407

PLANT SCRIPTS 3as that in the animal ? Is there to be found in plants anytissue that might twitch persistently, like the cardiac tissueof the animal ? If so, are these rhythmic pulsations charac-teristically similar ? Is there, again, any general resem-blance between responsive actions in plant and animal?Going deeper, since the same protoplasmic basis underliesthem both, are these reactions to be regarded as essentiallythe same, though different in degree ? If this last weretrue, then since the simpler explains the more complex,might not the physiological reactions of the plant be expectedto elucidate many of the obscurities in the similar reactionsof animal tissues ?We return, then, to the question, Is the plant capableof furnishing any such responsive indications as we havesupposed ? I have shown elsewhere that all plants giveresponse to impinging stimulus by a definite electricalchange, J which can be recorded by means of suitableapparatus. For the purpose of the present work, however,it will be convenient to employ the more conspicuous motileindications afforded by certain plants, pre-eminent amongstwhich is Mimosa pudica.

The most prominent motile organ in Mimosa consists ofa mass of tissue known as the pulvinus, at the joint or arti-culation of the primary leaf-stalk. The swollen mass on thelower side of this organ is very conspicuous. Under excita-tion the parenchyma, in this more effective lower half,undergoes ' contraction,' in consequence of which there isa fall of the leaf. This sudden movement constitutesthe mechanical response of the leaf to the impingingstimulus, just as the contractile movement of a muscle insimilar circumstances forms its characteristic mechanicalresponse.

Digressing for a moment to consider the phenomenonof excitatory contractions in general, it may be said thatour present knowledge is not complete as to the minutice

1 Bose : Friday Evening DiscourseRoyal Institution, May 1901Comparative ElectrO'Physiology, Longman's, London, 1907. B 2


32/407

4 RESEARCHES ON IRRITABILITY OF PLANTSof the process by which these are brought about. In muscleit is supposed that during the act of contraction there is atransfer and redistribution of fluid material. 1 In the case ofMimosa there is known to be an escape of fluid from theexcited cells ; there is a diminution of turgor. It is sup-posed that this may in some unknown way be connectedwith a diminution of pressure within the cell. 3

In the case of the stamens of Cynerece, Pfeffer 3 observeda contraction under excitation of as much as 30 per cent,of the original length. There is an escape of water fromthe cells into intercellular spaces. The mode in which thefall of turgor takes place is uncertain, and various supposi-tions have been made to account for it. It has been thoughtthat the escape of fluid is brought about by the elastic cellwall which forces liquid out of the cell, when the protoplasmlining it has become permeable under excitation. Theremay in addition be an active contraction of protoplasmwhich might force the liquid out of the cell-vacuole. Thislatter supposition is regarded by many as improbable,though the observations of Schiitt and Benecke indicatethat under stimulation the protoplasm of a diatom contractsaway from the cell wall. Similar withdrawal of protoplasm

1 ' Schafer, working on the highly differentiated wing-muscle of thewasp, concludes that each sarcomere contains a darker substance nearthe centre, divided into two parts by Hensen's disc. At each end of thesarcomere the contents are clear and hyaline. In the act of contractionthe clear material flows, according to Schafer, into tubular pores, in thecentral dark material.' Starling: Elements of Human Physiology,8th edition, p. 91.

'-' ' When the pressure in the cell decreases, we naturally assume thisto be due to decreasing osmotic pressure, a decrease which may wellamount to 2 to 5 atmospheres, and may be due either to the transformationof osmotically active substances into bodies with larger molecules, or toalterations in the permeability of the plasma, and an excretion of materialsfrom the cell. As evidence of excretion of material we may quote the factthat Pfeffer observed crystals of unknown nature appearing on evaporationof the liquid expressed from the intercellular spaces. Still there are severalreasons for doubting this conclusion. It is a remarkable fact that plasmo-lytic research affords no evidence of any decrease in osmotic pressure."Jost: Plant Physiology, English edition, 1907, p. 515.

aCf. Pfeffer : Physiology of Plants, vol. iii., English edition, p. 75.


33/407

PLANT SCRIPTS 5has been observed in Spirogyra by Nageli and in Nitellaby Hofmeister.Whatever theory may be held, the undoubted fact inthese two cases, of plant and animal alike, is the occurrenceof a fundamental excitatory protoplasmic change which findsexternal expression in alteration of form. If we nowrecord the responsive movement, we shall be recording" whatis an effect of excitatory change, either in plant or animal.Whether or not this fundamental change is similar in the twocases can only be decided by comparing the records due toexcitation, in plant and animal tissues, under all possiblevariations of external conditions.

The fall of the leaf of Mimosa is brought about inconsequence of the contraction of cells in the lower halfof the pulvinus. I shall for convenience describe the fallas the contractile movement, in contradistinction to theerectile movement brought about by the recovery of cellsinto normal turgid and expanded condition.

In studying the excitatory reactions of the plant, underexternal stimulus, we have to determine, first, what timeelapses between the incidence of the shock and the initia-tion of a perceptive responsive movement. This constitutesthe determination of the Latent Period. We have nextto find out at what rate this responsive movement of theleaf takes place, and after what time the contractile phaseof the movement is exhausted. After a short pausethe plant gradually recovers from the effect of the shock,and the leaf is re-erected to its former position. We there-fore Want to know the various rates at which recoverygradually takes place. In order to secure these data] itwill be necessary to make a graphic record of the entireresponsive movement of the plant organ. This record,further, must furnish us not only with the amount, but alsowith the time-relations, of this movement. This wouldinvolve the construction of a writing-lever which, deflectedby the pull of the falling leaf, would be capable of tracingon a writing-surface, moving at a known uniform rate, the


34/407

6 RESEARCHES ON IRRITABILITY OF PLANTSconcomitant curve. For this there must be an axis, sup-ported on frictionless jewelled bearings, and carrying twoarms of a horizontal lever and a thin vertical wire with abent tip, to serve as the writer. The different parts, as faras possible, should be made of aluminium, to secure theutmost lightness. A point of the petiole of the respondingleaf would be attached by a silk thread to one arm of thelever, the other having on it a small weight, to act as counter-

poise. On the fall of the leaf, under ex-citation, it would pull down with it theattached arm of the lever. The verticalwriter would then also move, say, tothe left. If the finely pointed bent endof the writer were to press lightlyagainst the smoked surface of a glassplate, which was allowed to fall, at auniform rate, by means of clockwork,a curve would then be traced whichwould not only record the responsivemovement and recovery but also givetheir time-relations (fig. i). To obtainthe latter, it would be necessary toknow the rate of movement of theplate on which successive vertical linesmight be traced by a time-marker atintervals of, say, one minute.

In order to find out the absolutemovement of the leaf we must know

the degree of magnification or reduction that has beeneffected by the recording arrangement. This will depend uponthe relative lengths of the writer and the lever, and thedistance of the point of attachment on the leaf from thepulvinus. When the lengths of the lever-arm and thewriter are equal, then the writer will describe a movementwhich is equal to that of the point of leaf-attachment. Byshortening the arm of the lever to half the length of thewriter, we should obtain the magnification of two. This

Fig. i.Diagrammaticrepresentation of Re-sponse Recorder.


35/407

PLANT SCRIPTS 7shortening might be accomplished by attaching the threadnearer to the fulcrum. Proceeding in the manner indicated,any magnification, however high, can be obtained.

Reduction, again, may be effected with equal ease.When the point of attachment is exactly midway betweenthe pulvinus and the tip of the leaf, then the movementexecuted by it will be half that described by the extremityof the leaf. By bringing the point of attachment nearer

Fig. 2.Response-curve of primary leaf of Mimosa ; the verticallines below the record indicate intervals of one minute each.

to the pulvinus, we can obtain whatever reduction may berequired.The resultant magnification or reduction of the record

will thus depend, in any given case, on two factorsnamely,the relation between the length of the writer and the lengthof the lever-arm, on the one hand ; and, on the other, therelation between the distance of the point of attachmentfrom the pulvinus and the entire length of the leaf.Thus if the lever produce a magnification of four, and thepoint of attachment cause a reduction to half, the resultingmagnification will be 4 X | = 2. As the movement of theprimary petiole of Mimosa is considerable, the records takenare normally either equal or reduced to two-thirds. Arecord taken in this manner is given in fig. 2. The height


36/407

8 RESEARCHES ON IRRITABILITY OF PLANTSof this curve gives the amplitude of the movement, andthe horizontal distance measures the corresponding time.The up-line here, a b, indicates the responsive fall, and thedescending line, b c, the gradual erection, due to recovery.The responsive movement was initiated within an exceedinglyshort time after the application of stimulusin this case anelectrical shockand the fall was completed also withina relatively short period. In a record which will be givenlater, taken on a faster-moving plate, these characteristicswill be seen better. The recovery, however, is a slow process,the earlier part being comparatively quick and becomingslower towards the end. The entire recovery is here seen torequire 12 minutes.

If we were able to apply a stimulus of exactly identicalintensity at regular and suitable intervals, and if the physio-logical condition of the responding tissue remained constant,then we should obtain a series of responsive twitches whichwould be practically identical. But if the physiologicalcondition were to undergo any change, under environmentalconditions, then the record would give us indications of thatinternal change, otherwise entirely beyond our power ofscrutiny. . Thus if the plant were to become depressed, theamplitude of the pulse would undergo a diminution. If onthe other hand its excitability should be enhanced, that factwould be indicated by an increase in the amplitude of theresponse.

The mere amplitude of the twitch, however, affordsonly a broad indication of the physiological condition ofthe tissue. There are many factors the effects of which findexpression in subtler changes of the response-curve. Oneagency, for instance, will make the plant more alert. Thisis at once reflected at that part of the curve which corre-sponds to the Latent Period. This becomes shorter. Theascent of the curve will also be more abrupt. Anotheragency will induce, let us say, a contrary change. Differentagencies, similarly, will bring about definite changes inthe contracting and relaxing portions of the curve. The


37/407

PLANT SCRIPTS 9varying effects of freshness and fatigue, of stimulating ordepressing drugs, of heat or cold, of the environment, arein this way clearly revealed by the characteristic flexuresof the curve. Thus, by means of testing-blows, we areable to make the plant itself describe those obscureinternal changes which would otherwise have entirelyescaped us.

In fact, the phytographic records would, in the caseof plants, supply us with all the information that myo-grams afford in the case of animal tissues. The experi-mental difficulties which the plant offers are, however,very great. In the case of muscle-contraction, the pullexerted is considerable and the friction offered by therecording-surface constitutes no essential difficulty, thougheven here the time-relations of the curve are, I have reasonto think, rendered somewhat unreliable by this friction.In the case of plants the contractile movement is relativelyfeeble, and in the movement of the leaflet of Desmodium, forinstance, a weight so small as four-hundredths of a gram isenough to arrest the pulsating leaflets. When employingthe very lightest lever, the extremely minute friction offeredby the smoked-glass surface of the recording-plate is sufficientin this case to cause complete cessation of the record.Even in the leaf of Mimosa, the friction offered is enough todistort the curve to such a serious extent that errors areintroduced into the amplitude and time-relations amountingto more than ^50 per cent. These difficulties have beenovercome by the successful devising of my ResonantRecorder, an account of which will form the subject of thenext chapter.

SummaryObscure modifications of internal condition of plant,

resulting from changing factors of environment, may berevealed by records of plant's response to testing-blows.

The relation between the impinging stimulus and the


38/407

io RESEARCHES ON IRRITABILITY OF PLANTSintensity of reply measures the physiological efficiency ofthe plant tissue for the time being.

Automatic records of mechanical and electrical responsesof plant can be obtained with suitable apparatus.

For recording the mechanical responses of Mimosa andother sensitive plants, a writing-lever is employed. Distor-tion of record by friction is apt to introduce error, whichhas to be eliminated.


39/407

CHAPTER IITHE RESONANT RECORDER

Advantages of intermittent contact in recordTwo types of apparatus :the Oscillating Recorder and the Resonant RecorderCoercer andVibratorPerfect tuningRecorders with standardised frequenciesSlide and clockworkThe record its own chronogramSmokedsurface and its fixationAdjustments of the writerRecords withcontinuous and intermittent contacts.

It was stated in the last chapter that however light thecontact may be, and however smooth the glass recording-surface, the record was still apt to be either arrested, orseriously distorted, on account of friction. As long as Iemployed the ordinary method of continuous contact ofthe writing-point with the glass surface, it was impossibleto overcome this particular difficulty. It occurred to me atlast that the problem might find a solution if I could succeedin making an intermittent instead of a continuous writing-contact. I have solved this problem by devising twodifferent types of apparatus, which I have called respectivelythe Oscillating Recorder and the Resonant Recorder. Inthe former, the 'recording-surface itself is made by anelectro-magnetic device, to vibrate to and fro, thus bring-ing it into periodic contact with the writing-point. 1 Thisapparatus is extremely convenient for the general pur-pose of recording responses in which the measurement ofexcessively short intervals of time is not essential.

But there are many important problems, such as thedetermination of the latent period, and accurate determina-tion of the velocity of transmission of excitation, in which

1 Bose : British Association Report, Dublin, 1908, p. 903.


40/407

12 RESEARCHES ON IRRITABILITY OF PLANTSwe require time-measurements of the order of one-hundredthof a second. It will be shown that these determinationscan be carried out with great precision, by means of theintermittent dots themselves, when the periodicity of theirrecurrence is rendered perfectly constant. For such pur-poses, then, we require a frequency of intermittent contactsamounting to something like a hundred times per second.

It was clearly impossible to make the heavy plate-carrier oscillate with such a high frequency. There remainedonly the theoretical alternative of causing the writing-point to vibrate to and fro, at the required frequency, soas to make the necessary intermittent contacts with thesurface of the recording-plate.

The advantage of this intermittence may be understoodfrom a concrete example. It will be remembered that thewriting-point, under the action of the responsive fall,moves parallel to the surface of the recording-plate. Ifnow, by means of some mechanism, the writing-point bemade to vibrate to and fro, say, ten times each second, atright angles to the plate, this will in no way affect the recordbeyond the fact that instead of a continuous line a dottedline will be traced. The record will not now labour underthe defects inseparable from the friction of continuouscontact. Instead of this, we shall have the vibrating writertapping a record which is practically free from friction.For it will be understood that, as in our concrete example, arecording-point which is vibrating ten times each second willexecute one entire to-and-fro movement in one-tenth of asecond. The duration of contact, at the extreme forwardend of the swing, will represent only a small fraction, sayone-fifth, of the entire period of one vibration. Henceafter each contact, lasting only one-fiftieth of a second, therecording-point is absolutely free to take up the movementimpressed upon it by the moving leaf. In a record lastingfor one second the sum of the intermittent contacts will thenamount to one-fifth, and the period of entire freedom tofour-fifths of a second. We can thus see the theoretical


41/407

THE RESONANT RECORDER 13advantages of an intermittent over a continuous contact.What has been said of the writer vibrating ten times ina second holds good equally in those cases where thevibration-frequency is much higher.

One great difficulty we encounter in carrying outthis idea lies in giving the recording-point an impulseexactly perpendicular to the direction of its recordingmovement. If the recording-writer be made of fine steel-wire, and if we place behind it a small electro-magnetthe pole consisting of a rectangular piece of soft iron, atright angles to the wirethen, by sending a momentarystrong current through this electro-magnet, a pull willbe exerted on the wire which will make its recording-tipstrike for an instant against the glass recording-surface.As the steel wire has to be made extremely fine, in orderto reduce to a minimum the inertia of the recorder, theresulting pull exerted on it is very slight, unless an exces-sively strong current be sent round the electro-magnet.Again, unless the intermittent closures of the electric circuitbe properly timed, the writing-index may be subjected toattraction in the course of its journey, now to the recording-surface and again away from it. In the latter of thesecases its vibration, on which the intermittent contactdepends, is totally destroyed.

But the most serious difficulty of all is that introducedby the edge of the attracting electro-magnet. It is knownthat the magnetic intensity of a pole is strongest at its edges.Should the writing-index by chance be placed exactlysymmetrically, as regards the right and left edges of thepole, then the two lateral pulls, being equal, will neutraliseeach other, and the index will vibrate to and fro perpendi-cularly to the recording-surface. But should it be placed,however slightly, nearer to one edge than to the other, thenone of the two pulls will be in excess, and the index willbe drawn to one side, thus producing a disturbance in therecord not due to the excitatory pull of the leaf. Evenif, at the beginning, the index had been placed in a


42/407

i4 RESEARCHES ON IRRITABILITY OF PLANTSstrictly symmetrical position, the movement of the writercaused by the excitation of the leaf would draw it into anasymmetrical position, resulting in a one-sided pull whichwould seriously interfere with the reliability of the record.

The Resonant RecorderIt is therefore absolutely necessary so to arrange matters

that the electro-magnet shall be without laterality. Thiscondition I was able to fulfil by making the pole of theelectro-magnet in the form of either a cylinder or a ring.The axis, from which is suspended the writing-index, isaccurately supported, perpendicular to the plane of thecircular section of the magnetic pole at its centre. Every-thing was thus made symmetrical, and as there was nolaterality there could be no tendency whatsoever for theindex to execute its to-and-fro vibrations in any otherdirection than that which was perpendicular to the planeof the terminal pole of the magnet. As this plane may beadjusted parallel to the glass recording-surface, the tappingmovement of the writing-index can be made to take placeperpendicularly to the recording-surface.

Next, in order to overcome the difficulty of the irregulartiming of those electrical impulses which are to maintainthe recording-index or writer in a state of periodic vibra-tion, I devised the Resonant Recorder. If we know thenatural frequency of vibration of the recording-index, andif by means of some mechanism we can send periodiccurrents of exactly the same frequency through the electro-magnet, then the intermittent magnetic pulls will exactlysynchronise with the natural swings of the writing-index.Owing to this perfect tuning the index will now resonate,breaking out into a persistent and regular vibration of con-siderable amplitude. In practice, all that is necessary inorder to secure this is to take a long steel reed, which in thecourse of its regular vibration will periodically interruptthe electro-magnet circuit of the vibrator coil. The reed


43/407

THE RESONANT RECORDER 15itself is maintained in a state of persistent vibration by theusual electro-magnetic arrangement, I shall for the sakeof convenience refer to this reed-interrupter as the Coercer ;and the writing-index simply as the vibrating-recorder orVibrator. The reed was at first purposely selected of toogreat a length, so that the natural frequency of the coercershould be slower than that of the vibrator. The free endof the coercing reed carries a platinum wire which, dippinginto a cup of mercury, completes the electric circuit. Theother end is clamped, and by shifting the clamping-pointthe vibrating length of the reed is gradually and continuouslyshortened. This has the effect of gradually raising thevibration-frequency of the interrupting reed. A time sooncomes when the frequency of the coercer is exactly thesame as that of the vibrator. The latter, which has beenhitherto more or less inert, now suddenly breaks out, asforeseen, into very regular and sustained vibrations of largeamplitude. For some purposes it is important that thevibration-frequency of the recording-index should have adefinite value. The various frequencies most suitable forthese researches were 10, 20, 50, 100, and 200 vibrationsper second. The exciting reed was previously calibratedby means of frequency-meters, or standard tuning-forks, togive these values. Then, with great expenditure of timeand patience, different vibrating-recorders having variousstandardised frequencies were constructed. For this wehave to select fine-steel wires of differing lengths and thick-nesses. The final tuning is accomplished by careful filingor hammering. Filing the tip of the vibrator raises thefrequency ; and hammering of the wire, near the point ofsuspension, lowers it. A general flattening, along the wholelength, tends to maintain the vibration in a definite plane,otherwise the free tip is apt to execute an elliptical vibration.The tuning of the vibrator with the coercer is not verydifficult when the vibration-frequency is low, say 10 persecond. But when the frequency is high, say 100 or 200 timesin a second, an exact tuning is essential. The slightest


44/407

16 RESEARCHES ON IRRITABILITY OF PLANTSvariation of the length of the coercer will either bring aboutfull resonance or make it entirely ineffective. When thetuning is nearly but not quite perfect, then we have thephenomenon of beats. In this case, in the successive dotsof the record, there will be periodic blanks. For the purposeof exact adjustment of length of the coercer I employ amicrometer-screw, by means of which the most delicateadjustment of length may be carried out.

For periodic interruption the coercing and vibratingcoils may be put in series, but I find it is much easier toobtain a persistent vibration when the coercer coil is placedin a multiple arc with the vibrator coil. An electro-motiveforce of 4 volts should be sufficient for the purpose of maintain-ing a steady vibration of both the coercer and the vibrator.

Having thus secured the requisite perfection of theresonating-writer, it is necessary to describe the completeapparatus by which to obtain records of responses in Mimosaand other sensitive plants. For this purpose we require aslide-carrier to hold the recording-plate, and this is to bedropped at a definite speed, without jar ; also the clockworkby which it is to be actuated. Besides these is needed somespecial means by which the recording-point may be broughtto the proper distance from the recording-surface. It isnecessary, again, that the response-movement of the writershould be absolutely parallel to the writing-surface, and thatits tip or contact-point should be capable of delicate adjust-ment as regards distance. It should be possible, moreover,to bring this writing-point to any position on the recording-surface that may be required. I will now proceed to relatethe devices by means of which all these conditions have beenmet. Some of these will be seen in fig. 3, which illustratesonly the upper part of the Resonant Recorder.

The Slide and ClockworkA gunmetal upright, the upper part of which is of trian-

gular section, stands on a large disc of the same metal, whichis screwed to a larger wooden base-board. The slide-carrier,


45/407

THE RESONANT RECORDER 17holding the glass recording-plate, moves up and down thetop part of the upright. It is essential to have this slide soaccurately fitted that the plate-carrier may be able to drop

cm

Fig. 3.Upper part of Resonant Recorder. (From a Photograph.)Thread from clock,' not shown, passes over pulley p, letting down

recording-plate ; s', screw for adjusting distance of writing-pointfrom plate; s, screw for vertical adjustment; t, tangent-screwfor exact adjustment of plane of movement of recorder, parallel towriting-surface ; axis of writer supported perpendicularly at centreof circular end of magnet ; c, coercer ; m, micrometer-screw foradjustment of length of coercer; v, vibrating recorder ; G, smoked-glass plate.

smoothly and uniformly, without any jerking whatsoever.I have sometimes attained the same end by mounting theplate-carrier on wheels and letting it slide down vertical rails.The plate-carrier is allowed to drop by the running down of


46/407

i8 RESEARCHES ON IRRITABILITY OF PLANTSa clock or a phonograph motor, according to what maybe the requirement of the speed. The quarter-plate size(n X 8 cm.) is convenient for record, as it is not too largefor book illustration. The suspending thread passing overpulleys is wound round the winding-wheel of the clock. Thiswheel is provided with click and ratchet, which allow it tobe wound without interfering with the axis of the clock.Thus winding of the wheel in the left-handed direction pullsup the recording-slide. The running-down of the clock thenallows the slide to fall at a uniform rate. The variousspeeds found necessary for different records were such thatthe entire length of the plate, n cm., travelled past therecording-point in .5 second, 6 seconds, 15 minutes, 1 hour,or 3 hours. The first two of these rates were obtained froma phonograph motor employing two different-sized wheels.The last three were obtained by attaching three different-sized wheels to the clock-axis which carries the minute-hand.In these slow rates the movement of the plate is quite uniformfrom the beginning, but when, as in the first two cases, thishas to be dropped at a relatively high speed, a short timewill elapse, equivalent at most to the first fourth of theplate, before it becomes quite uniform. Should uniformityof such movement be specially desired for the record, it mustbe commenced after passing this first fourth. But on accountof the chronographic signals which accompany the record,this uniformity is not absolutely essential, for they giveus the data from which the time-relations of the curvemay be derived.

I may here refer to a few practical points with regardto the preparation of the glass for record and its subse-quent fixing. In order to produce an even layer of smokeon the recording-plate, it is moved over the gas-flamefrom a bat's-wing burner ; and this deposit of smoke willbe improved if the gas has been previously passed througha jar containing a small quantity of benzine. After therecord is taken, it is fixed by pouring carefully overit a dilute solution of Canada balsam in xylol. It is


47/407

THE RESONANT RECORDER 19afterwards easy to reproduce this record by contact-printon a photographic paper.

Adjustment of the WriterIt is sometimes necessary to have the recording-point

brought two or more times to the same place, in orderthat the successive records may be rendered the morestrictly comparable. This is accomplished by a rack andpinion to adjust the height of the platform carrying theplant. When the platform is lowered, the petiole, whichis attached to one arm of the recording-lever, pulls it down,and the recording-point is moved to the left. When theplatform is raised, then by the action of the counterpoiseattached to the other arm of the lever the index is movedin the opposite direction. In this way the recording-pointcan be brought to any position that is desired. The sameend is secured through adjustments of a micrometer bywhich the carrier of the writing-index is raised or lowered.

Another adjustment that is necessary is the bringingof the recording-point near to the writing-surface withoutactual contact ; so that, when the index is set in a stateof resonance, it may trace a dotted line. The necessaryadjustment is brought about by means of a micrometer-screwat the top of the instrument, by which the lever can be madeto approach or recede from the writing-surface. When thespeed of the plate is slow, the successive dots may be soclose together as to appear like a continuous line.

More troublesome is the adjustment necessary to renderthe plane of movement of the index exactly parallel to thewriting-surface. If this be omitted, the writing-point inone part of the record, say to the right, will be too faraway to strike the surface, whereas in another part, sayto the left, it will press against the plate and lose its freedom.This difficulty I have been able to overcome by mountingthe vertical rod, carrying the writer, inside another tube. Anattached tangent-screw, t, then causes a very slow rotation


48/407

20 RESEARCHES ON IRRITABILITY OF PLANTSof the vertical rod, either in the right-hand or the left-hand direction. By this means it is possible to bring the

Fig. 4.General view of the whole apparatus, and the electrical connec-tions by means of which excitatory shock of a definite duration maybe given to the plant ; duration of shock determined by metronomewhich completes electrical circuit. (From a Photograph.)

plane of movement of the writing-index exactly parallel tothat of the writing-surface. The complete apparatus for


49/407

THE RESONANT RECORDER 21obtaining response of Mimosa is shown in the accompanyingillustration (fig. 4).

Having thus given an account, in some detail, of thepractical working of the Resonant Recorder, it will nowbe well to show a pair of curves which demonstrate, ina marked manner, the advantage of intermittent overcontinuous contact in the making of these records (fig. 5).These represent two successive experiments on the sameleaf, under identical stimulation of an electrical shock.The recording-plate washere moving at a mode-rately high speed. Thelower record was takenwith continuous con-tact, and the upperwith the same recorderbut in a state of vibra-tion, giving intermittentcontact. The vibration-frequency was 10 timesper second. Stimuluswas applied at the pointmarked by the verticalline. A comparison ofthe two records willshow that owing to therelative loss of freedom,due to friction, in thecontinuous contact, the latent period, or the intervalbetween stimulus and initiation of response, is prolongedand the amplitude of the response itself reduced. In thecase of the intermittent contact, on the other hand, we seethat besides the freedom from this particular error we havethe further advantage that the record itself contains itsown time-marks, the successive dots being at intervals ofone-tenth of a second.We have next to consider the practicability of devising,

Fig. 5.Advantage of intermittent overcontinuous contact in obtaining re-cords.


50/407

22 RESEARCHES ON IRRITABILITY OF PLANTSfor the excitation of the plant tissue, perfect methods ofstimulation, the intensity of which can either be maintainedconstant or varied in a perfectly known manner. Wehave moreover to render the successive stimulations, andconsequent scripts of the plant, a perfectly automaticprocess ; so that the experimenter may be comparativelyrelieved of personal participation in the securing of therecords. This will have the incomparable advantage ofhaving no element of personal error in the results soobtained. The question of the effects of the various formsof stimulus will be dealt with in the next chapter.

SummaryIn the response-records of plants, errors are introduced

on account of friction of the writing-point against therecording-surface.

These errors are eliminated by the method of intermittentinstead of continuous contact for the record. By employ-ing the principle of resonance, the writer is made to vibrateto and fro at a known and definite rate. The record consistsof series of dots giving definite time-intervals. The recordis thus its own chronogram.


51/407

CHAPTER IIIMETHODS OF STIMULATION

Different methods of stimulating the plant : mechanical, chemical, thermal,and electricalDifficulties of securing quantitative stimuliDirectand indirect stimulationIdeal modes of stimulationElectro-thermic stimulationStimulation by constant currentStimulationby condenser-dischargeNon-polarisable electrodesDirect, extra-electrodal, and intra-electrodal stimulationStimulation by inductionshockEffects of make- and break-shockExcitation by tetanisingshock.

In the case of contractile animal muscle, various stimuligive rise to excitation, and it is a very remarkable fact thatthe same stimuli exercise a similar excitatory influenceon the pulvinus of Mimosa. Classifying these stimuli,we find that they are :

1. Mechanical.A blow will excite animal muscle andcause mechanical response. A similar effect is induced bya mechanical blow in the pulvinus of Mimosa. A prick orcut also will cause contraction in either.

2. Chemical. Various chemical agents are found toinduce excitation in botl* animal and vegetal contractiletissues. Thus dilute hydrochloric acid or ammonia causesexcitation of both muscle and pulvinus.

3. Thermal.The application of a hot wire will induceresponsive contraction in both cases.

4. Electrical.The muscle may be excited by an induc-tion-shock. The pulvinus of Mimosa is also excited bysuch shocks. Other modes of electrical stimulation, suchas that of condenser-discharge and that of the applica-tion of a constant electrical current, are found effective incausing excitation of animal tissues. It will be seen in the

23


52/407

24 RESEARCHES ON IRRITABILITY OF PLANTScourse of the present chapter that plant tissues also may beexcited by similar methods.

In all these cases excitation may be either direct orindirect. In the case of muscle, with its attached nerve,we may cause excitation directly by applying the variousforms of stimulus on the muscle itself, or indirectly byapplying them on the nerve. In the latter case excitationis transmitted by the conducting-tractthe nerveandreaching the muscle after a brief and definite interval,induces there the usual contraction.

Taking the case of Mimosa, we may similarly haveeither direct or indirect excitation. Excitation is directwhen it is applied, say, on the contractile pulvinus itself.It is indirect when it is applied on the petiole, at a distancefrom the pulvinus. Certain tissues in the petiole conductthis excitation, which, reaching the pulvinus after a definiteinterval, induces a responsive contraction.

It is usually maintained that in the case of Mimosathere is no true conduction of excitation, but that this con-tention is not justified will be fully demonstrated in a sub-sequent chapter. We have, then, in correspondence to thenerve and muscle preparations of the animal, plant-speci-mens, consisting of petiole and pulvinus. Indirect excitationfor specific experiments is effected in the animal throughthe nerve, and in the plant through conducting-strandsembedded in a tissue, as in the petiole.

Although we thus have various forms of stimulus at ourdisposal for inducing individual and isolated responsivecontractions in Mimosa, yet we are confronted with verygreat difficulties when we wish to obtain a series of uniformexcitations for quantitative investigation. It is obviousthat chemical forms of stimulus would be impossible forsuccessive excitations. The objection to a mechanicalblow, as the stimulus to be employed, lies in its liabilityto cause a mechanical jar and thus to disturb the record.

The ideal form of stimulation would be one the inten-sity of which might be maintained uniform in successive


53/407

METHODS OF STIMULATION 25experiments, or varied in a definite and known manner.Another great obstacle to be overcome in practice is theavoidance of injury which is caused by the stimulus itself.The application of stimulus above a critical intensity inducesa depression or abolition of excitability of the tissue.

As the result of long investigation for the purpose ofsecuring various forms of quantitative stimulus, I findthat one mode of thermal and three modes of electricalstimulation may be rendered practicable for our purpose.These four different methods will be described in somedetail below.

Electro-thermic StimulationIt is evident that touching the specimen with a hot

wire, though effective, is not a form of stimulus that iscapable of quantitative application or of repetition. It isapt, moreover, unlessvery great precautionsare taken, to injure thetissue.

The thermal mode ofstimulation can, how-ever, be rendered prac-ticable by the electricalmode of the generationof heat. A loop of fineplatinum-wire is madeto clasp round the peti-ole which is to be ex-cited, and is connectedwith an electrical circuit by means of fine flexible silver-wire(fig. 6) . The circuit can be completed by a metronome inter-rupter, the current from the battery flowing for a definitelength of time during, say, a single or definite number of beatsof the metronome. This produces a sudden thermal shock,enough to cause excitation. Successive uniform stimuli can

Fig. 6.Electro-thermic stimulator foruniform stimulation ; metronome em-ployed in place of key k, for closingcircuit for definite length of time.


54/407

26 RESEARCHES ON IRRITABILITY OF PLANTSthus be applied. By means of a variable resistance includedin the circuit, the intensity of the stimulus can be increased ordiminished. Care must, however, be taken that the heatproduced in the platinum loop shall not be such as to scorchor otherwise injure the tissue.

I find that injury from scorching may be avoided byadding a drop of water at the point of contact and after-wards removing excess of water by blotting-paper. Thisthin film of water protects the tissue from a burn. It is,again, not absolutely necessary to place the platinum wire

in contact with the plant.Excitation will take placeif the heating-wire is inclose proximity. Howpracticable this form ofstimulus may be renderedwill be observed from therecord (fig. 7) of two suc-cessive excitations by thismethod, which are seen tobe uniform. For certainFig. 7.Response records of Mimosa . . . . .

under indirect thermal stimulation. electrical investigations itis essential that stimulus

other than electrical should be employed. This require-ment is admirably fulfilled by the thermal mode of stimu-lation.

Another mode of stimulationnamely, that of thermalradiationcan also be employed, though not so convenientlyas the former. A certain area may be rendered radiant by thepassage of an electrical current. A Nernst electrical lampcan be conveniently utilised for the purpose. This, whenrendered incandescent, gives out radiation of constantintensity. This radiation consists not only of light raysbut also of a large proportion of obscure heat-rays. Theexcitatory value of the latter is more efficient than theluminous rays. The radiant surface of the Nernst lampis suitably placed in front of a concave metal mirror, by


55/407

METHODS OF STIMULATION 27means of which the rays can be focused upon any point thatis desired.

Stimulation by Constant CurrentI have found that Mimosa and other sensitive plants show-

certain very remarkable excitatory effects under the actionof a constant current. The characteristic feature of theseis that excitation is not induced during the passage of thecurrent but only at its initiation or cessation. The excita-tory effect in this case is further conditioned by the point

Fig. 8.Responses to stimulation by constantelectric current.

of entry, or anode, and that of exit, or kathode. Thespecific characteristics of this mode of stimulation will befound fully described in the chapter on the Polar Effectsof Currents in Excitation. It need only be mentioned herethat, in the matter of all these peculiar effects, the planttissue behaves in a manner exactly similar to the animaltissue. A series of records obtained from Mimosa by thestimulus of a constant current are shown in fig. 8.

Stimulation by Condenser DischargeAnother practical method of stimulation is that of

condenser discharge. The condenser consists essentiallyof two conducting-plateswhich may be two sheets of


56/407

28 RESEARCHES ON IRRITABILITY OF PLANTStin-foilseparated by a sheet of non-conducting material,such as mica or paraffined paper. The capacity of thecondenser is increased by enlarging the effective area ofthe plates. The diagram in fig. 9 illustrates this mode ofexcitation. By increasing the number of cells, the charginge.m.f. may be increased until a suitable value is obtainedwhich is efficient for excitation. This will depend on theexcitability of the plant-specimen. About 2 volts charging5 microfarad will in general be found sufficient, k is aspecial spring-key by which the condenser may be charged

Fig. 9.Direct stimulation by condenser discharge ; c, condenser, k,key. (a) intra-electrodal and (b) indirect extra-electrodal mode ofstimulation.

or discharged. The plant to be excited is included in theelectrical circuit. When k is pressed down, the condenseris charged, the instantaneous charging current passing inone direction. The upper arrow in the diagram showsthe direction of this charging current. When the key isreleased, it springs back and discharges the condenser.The instantaneous discharge current now flows in a reversedirection (fig. 9).The electrical connections with the plant are diagra-matically shown, in this and other figures, by two lines.In practice the connections have to be made by meansof thread moistened in dilute saline solution. In certainexperiments it is necessary to avoid complications arisingfrom electrolytic polarisation. In these it is advisable to


57/407

METHODS OF STIMULATION 29use non-polarisable electrodes for making the connectionswith the plant tissue. Such non-polarisable electrodesmay be of the usual U-tube type. The shorter limb of theglass U-tube is filled with kaolin paste in normal saline.A cotton thread moistened in saline protrudes from thisand makes the connections with the tissue. The longerlimb is filled with zinc sulphate solution, into which dipsa zinc rod. For ordinary purposes, however, a much simplercontrivance is found effective. A narrow cork is partiallyhollowed out and paraffined. The well thus formed isfilled with dilute saline solution. The bottom is piercedfor the entry of a cotton thread into the saline. A thicksilver-wire, whose surface has been covered electrolyticallywith a film of chloride, pierces the side of the cork anddips into the saline solution. The silver wire forms oneof the two electrodes, and the cotton thread makes thenecessary electrical connection with the tissue.

For the purpose of excitation we may make the twoelectrical connections, one at or near the pulvinus itself, andthe other on the petiole at a short distance. It will be shownlater that when the electrical current leaves the tissue bythe pulvinus, that point becomes the seat of excitation.Thus by making the pulvinus the point of exit of current,or kathode, we may cause direct excitation. Or we mayhave the pulvinus included between the two electrodes, sothat the electrical current passes through it (fig. 9, a). Thisconnection we may designate the intra-electrodal. Here, incertain circumstances, the excitation throughout the tractbecomes diffuse and practically instantaneous. And lastly,the two electrical connections may be made side by side,say about 1 cm. apart on the petiole, at a moderate distancefrom the pulvinus. The excitation thus caused in thepetiole reaches the pulvinus, as I have already said, byconduction. This connection we may call extra-electrodal(fig- 9, b).

I give below a series of records (fig. 10) of response tostimulation by condenser discharge. The plant was highly


58/407

30 RESEARCHES ON IRRITABILITY OF PLANTSexcitable, and excitation was caused by the discharge ofi microfarad condenser charged to -3 volt.

Stimulation by Induction-shockExcitation may be induced by means of a single or

repeated shock from an induction coil. In my own expe-rience I was at first under the impression that this mode ofstimulation was not suitable for repeated quantitativeexperiments, as I found that the plant was liable to becomeinsensitive owing to the fatigue or injury caused by the shock.Later, however, I was able to trace this difficulty to the

Fig. 10.Record of responses to stimulation bycondenser discharge.

employment of an intensity of shock which was in excessof a certain critical value. I had in fact been misled bythe prevailing belief that the excitability of the plantwas considerably lower than that of the animal. HenceI employed an intensity of current which was unnecessarilyhigh. This induced fatigue and consequent insensitiveness.Afterwards I discovered that in so far as its sensitivenessto electrical stimulation was concerned, Mimosa was in noway inferior to the animal. Quantitative results will begiven later, in justification of this statement. Avoiding,then, an intensity of stimulus which was too great, andallowing proper resting-intervals, I found that the efficiencyof induction-shock as a mode of stimulation was all thatcould be desired. It has also the great advantage of


59/407

METHODS OF STIMULATION 31allowing successive stimuli to be maintained constant, orto be increased in a known manner.The induction coil consists of a primary made of afew turns of thick wire enclosing a bundle of soft ironwirethus forming an electro-magnetand of a secondaryconsisting of a larger number of turns of thin wire. Thesecondary coil can be made to approach or recede fromthe primary, by means of a slide. When a current issuddenly started in the primary coil, by pressing a key aninstantaneous make-induction-current is induced in thesecondary. When, by releasing the key, this currentis broken, an instantaneous break-induction-current, whosedirection is opposite to that of make, is induced in thesecondary. Owing to the greater suddenness with whichthe break is effected, the intensity of the break-shock isgreater and of shorter duration than that of the make-shock.The intensity of either make- or break-shock may be in-creased by bringing the secondary nearer the primary.We can obtain successive uniform shocks, of either makeor break, by maintaining the distance between the twocoils constant.We may subject the tissue to shock of either make orbreak at will by employing an additional short-circuitingkey. When this key is down, the shock from the secondarycoil is practically diverted across the better conducting-path provided by the key, so that for practical purposesnone passes through the plant tissue. If it is desired tocause successive excitations by make-shock only, then theshort-circuit key is raised when the primary circuit is made,and pressed down when this is broken. For exciting bybreak-shock, the short-circuit key is pressed when the primaryis made and raised when the primary is broken (fig. 11).

Effects of Make- and Break-shockIn the response of animal tissue it is well known that

while single induction-shocks are effective in the case ofquickly reacting skeletal muscles, they induce hardly any

8/6/2019 Researches on Irritability of Plants Sir J

Documents

Researches on Irritability of Plants Sir J C Bose